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LOS ANGELES (AP) — Tuna, the hound so homely he's irresistible, peeks out from beneath his blanket, baring his row of buck teeth in a slapstick smile for the camera.

Courtney Dasher of Los Angeles rescued the Chihuahua-dachshund mix with the bug eyes, big nose and infamous overbite in 2010. Four years later, the dog dubbed a "Chiweenie" in hashtags has 837,138 followers as of Tuesday night, when he ranked as the most-popular dog on Instagram.

Pet owners are unleashing their pooches on the photo-sharing service, setting up accounts to show Manny the French bulldog sporting spectacles or Tuna poking his schnoz out of a suitcase.

Funny pet photos continue to be a trend on social media. They get plenty of play on Facebook and Twitter, including "muttbombs," where people Photoshop dogs into snapshots of themselves or celebrities. Muttbombs and animal Instagram accounts are so popular that shelters and others use them to promote adoptions or rescue campaigns. These famous pooches also have been featured in shelter public service announcements and swarmed by fans in public.

That's because animal lovers eat up the snapshots of dogs doing the darndest things, giving Manny and Tuna insta-fame on Instagram.

Dasher, who says Tuna resembles Mr. Burns from "The Simpsons," started @tunameltsmyheart in 2011.

"You would never hear me call Tuna ugly," Instagram spokeswoman Liz Shepherd said. "He has unconventional beauty. Some people say Tuna is the best part of their day."

Handsome is the word Dasher uses. "He's so unique, and I love that and everything about him," she said.

For Manny, the dog once rejected by a breeder is now the world's most followed French bulldog on Instagram, with 502,594 people subscribing to @manny_the_frenchie as of Tuesday night. Amber Chavez of Chicago says her dog looks like a cross between a bunny and a piggy, and he is the fourth-most-followed pooch on the social network.

"He was like a first-born child, we couldn't stop photographing him," Chavez said, who set up the account with a friend in 2012. "We wanted to share pictures with family and friends and saw other animals had their own Instagram pages, so we created his very own."

Manny's owners are among the many who use their dog's account to aid animal charities.

Loni Edwards of New York City follows Manny, who has been posed to look like he's sipping a soda and dressed up to resemble hip-hop artist Pharrell. She said silly or cute canine antics put her in a good mood, and there's plenty of that from Manny, who spins on his back legs to a rap song in one short Instagram video.

"I have a thing for Frenchies," Edwards said, explaining why she got Chloe, who has her own page, @chloe_theminifrenchie.

Chavez and Dasher say motivation for their posts comes from their dogs or the fans.